The present invention generally relates to node apparatuses, and more particularly to a node apparatus of a communication network employing a multi-conjunction architecture.
A multi-channel lattice communication network applicable to local area networks (LANs), public line networks and especially to a multi-media communication was previously proposed in a U.S. patent application Ser. No. 096,532 filed Sept. 15, 1987 in which the assignee is the same as the assignee of the present application. The proposed lattice communication network is analogous to nerve cells of a living body, and employs node apparatuses. Each node apparatus has a plurality of input and output channels and is used as a communication control element. Such node apparatuses are coupled in a multi-conjunction to constitute the lattice communication network. Each node apparatus transfers one of incoming digital signals according to a first-come-first-served logic (hereinafter simply referred to as a first-come-first-output logic).
The proposed lattice communication network has a large degree of freedom of network topology because of the multi-conjunction architecture. Thus, the survivability of data is high. In other words, even when a fault occurs in a path of the communication network, it is possible to carry out the communication through other paths. Furthermore, it is possible to select optimum paths for the communication because each node apparatus transfers the incoming digital signals according to the first-come-first-output logic.
On the other hand, the proposed lattice communication network employs a multi-channel system in which a plurality of connecting channels are established, so as to effectively achieve a full duplex communication. The proposed lattice communication network is effectively applicable to the physical layer to the network layer of the open system interconnection (OSI), for example.
When making a communication in the proposed lattice communication network, a node apparatus which receives a signal broadcasts the signal to other node apparatuses or terminal devices and waits for an acknowledge signal or returning signal sent back from a destination terminal device. A communication path is fixed when the acknowledge signal is received from the destination terminal device. The fixed communication path is supervised by each node apparatus included in the fixed communication path. Each node apparatus constantly supervises the signal level at input and output channels thereof, and detects an end of the communication when a low level continues for a predetermined supervision time. The node apparatus enters an end sequence when the end of the communication is detected.
Generally, the node apparatus is used in common for communications of different protocols. A supervision time based on which the end of the communication is detected is generally different for each protocol. However, in the proposed node apparatus, the supervision time for use in detecting the end of the communication is fixed. For this reason, in order to enable communications of different protocols to be made through the one node apparatus, the supervision time of the node apparatus for use in detecting the end of the communication must be set in accordance with the protocol which requires the longest supervision time. In this case, unless the supervision time is set to the longest supervision time, there is a danger in that a low-level information signal in the communication path may be erroneously detected as an end of the communication and result in an erroneous disconnection of the communication path while a communication is actually being made.
However, when the supervision time of the node apparatus is set to the longest supervision time, it takes this longest supervision time to detect an end of a communication of a certain protocol which may actually be detected within a shorter time. In this case, the releasing of the fixed communication path is unnecessarily prolonged. Furthermore, the traffic of the communication network as a whole is unnecessarily limited.